Some conventional PLLs lock a voltage controlled oscillator (VCO) to an externally provided reference frequency. In some systems, VCO output is divided before being compared to the reference frequency. The PLL locks the VCO to a multiple of the reference frequency. In these systems, this locking is accomplished by adjusting a control voltage of the VCO until a phase of a divider output matches a phase of the reference. Once the phases match, the frequency ratio must match the divider value.